German Published Patent Application No. 197 35 665 describes a fuel injection system which has a compensating element made of a supporting body having a dome-shaped supporting surface. This compensating element supports a fuel injector in a receiving bore of a cylinder head. Since the fuel injector rests on the spherically shaped calotte surface by way of a supporting surface, the fuel injector can be mounted at an angle that deviates from the axis of the receiving bore by up to a certain amount, and can be pressed firmly into the receiving bore using appropriate means, e.g., a clamping shoe. This allows a simple adaptation to be made to the fuel supply lines. Tolerances arising in the manufacture and in the mounting of the fuel injectors can be compensated for.
It is disadvantageous, however, that the supporting body requires expensive manufacturing and that a precisely manufactured, spherical surface is needed. The rigid supporting body cannot be compressed, and thus no compensation in the axial direction of the receiving bore occurs. Moreover, tolerance can only be compensated with respect to the specified geometry of the spherical surface. A radial compensation movement purely with respect to the receiving bore is not possible.
A system described in German Published Patent Application No. 197 35 665, for forming the spherical surface on the cylinder head itself and thus, obviating a separate component part, has the additional disadvantage that the spherical surface requiring a high degree of accuracy must be formed in a bore, at the relatively large workpiece for the entire cylinder head. This has disadvantages from the standpoint of production engineering.
German Published Patent Application No. 197 35 665 describes an intermediate piece on an inlet side of a fuel injector, in order to compensate for tolerances with respect to the axes of the fuel injector and a fuel-outlet orifice of a fuel-distributor line. In this context, a nozzle body of the fuel injector is inserted into a receiving borehole of a cylinder head, and is held by suitable retaining means, e.g. a clamping shoe, which means that the position of the fuel-injector axis is preselected. A possible axial offset between the axis of the fuel injector and the axis of the fuel-outlet orifice of the fuel-distributor line is compensated for by tilting of the intermediate piece positioned between the axes. In each case, this intermediate piece is sealed by a sealing ring in a direction of the fuel-distributor line, as well as in a direction of the fuel injector.
It may be disadvantageous to have the additional expenditure associated with having several more components, and to have the additional number of connections to be sealed. Since the intermediate piece requires an increased overall height, it can only be designed to be relatively short. This results in the need for the intermediate piece to already be at a relatively large angle to the axes, even when the axial offset to be adjusted is small. However, in the case of bending, the seal of the sealing ring between the fuel injector and the intermediate piece, on one hand, and between the fuel-outlet orifice and the intermediate piece, on the other hand, is based only on the elasticity of the respective sealing ring. Therefore, there is the danger of the sealing rings not being uniformly compressed between the respective sealing surfaces, when the angle is too large. This can result in leakage.
A thermal protection sleeve is described in German Published Patent Application No. 197 43 103, which encircles a fuel injector at a nozzle body. The thermal protection sleeve is inserted into a stepped receiving borehole of a cylinder head of an internal combustion engine, and circumferentially surrounds an ejection-side nozzle body segment of a fuel injector inserted into the receiving borehole. One end of the thermal protection sleeve has a collar, which rests against a step of the receiving borehole. In addition, the ejection-side end of the thermal protection sleeve has a folded section, which renders a certain length of the sleeve double-layered. In this region, the sleeve is radially locked between the nozzle body and the bore in the cylinder head. Since a tapered segment of the thermal protection sleeve, against which a likewise tapering segment of the fuel injector rests, is adjacent to the double-layered segment in the direction of the fuel supply line of the fuel injector, a certain transfer of axial force from the nozzle body of the fuel injector to the thermal protection sleeve is possible.
However, this does not allow adjustment of the tolerances of the position of the fuel injector in the receiving borehole. Furthermore, the fuel injector rests against a beveled step of the receiving bore, thereby completely determining the axial position of the fuel injector.